The present invention relates to video recording and in particular to reproducing still pictures recorded along slant tracks on magnetic video tape.
When reproducing still pictures recorded on slant tracks on magnetic tape it is common practice to repeatedly scan the same slant track with the rotating head or heads. This is particularly true for the widely used devices wherein a field is recorded per slant track with two 180.degree. offset video heads. The two video heads scan the same slant track in sequence and repeatedly. However, the signal-to-noise ratio with such devices is reduced when the magnetic tape is idle as compared to when the tape is moving since the scanning device of the video heads is not in conformity with the recorded tracks. This is illustrated in FIG. 1 wherein tracks 2 and 3 depict the tracks recorded (or scanned) by a video head when the tape is in motion and track 4 depicts a track recorded (or scanned) when the tape is stopped.
Heretofore, several proposals to eliminate the error resulting from the above have been proposed. For example, the angle of inclination of the total slant track cylinder may be changed so that the video heads follow the recorded tracks 2 and 3, even when the tape is idle. This is suggested in U.S. Pat. No. 3,375,331. French Pat. No. 2,107,066 suggests the vertical adjustment of the tape feed at the slant track cylinder. IBM Technical Disclosure Bulletin, June 1969, pages 33/34 suggests reciprocal movement of the video heads axially during each rotation of the head. Unfortunately, none of the above can be employed if for tape saving purposes, the slant tracks are recorded immediately adjacent to each other without any guard band and if they are recorded with different azimuth angles in order to eliminate cross talk. For example, a known device uses two video heads for recording and reproducing, wherein the azimuth angle of the gap of the one video head is 15.degree. in clockwise direction and the azimuth angle of the gap of the other video head is 15.degree. in counterclockwise direction. With this embodiment it is impossible to obtain a distortion-free still picture recording by means of repeated scanning of the same track, even if one of the above mentioned means for compensating for the differing angle between the scanning direction of the heads and the inclination of the recorded track is used.
In view of the above, it is an object of the present invention to provide a method to permit distortion-free still picture reproduction with such slant track devices, wherein adjacent slant tracks are recorded and scanned without a guard band therebetween and with different azimuth angles.